The present invention is directed to methods for grinding and mixing edible fat-based slurries and emulsions in a vibratory media mill. The invention has particular application to the field of manufacture of chocolate. The present invention can be used advantageously to grind and mix any edible fat-based slurry or emulsion, but has special application in manufacturing chocolate.
Generally, chocolate is a dispersion or emulsion of very fine, solid ingredient particles suspended in a fat phase. (As used herein, an “emulsion” refers to a finely divided phase dispersed in a dissimilar continuous phase, including dispersions of finely divided solid particles in a continuous fat phase (such as in chocolate), oil-in-water (O/W) emulsions, water-in-oil (W/O emulsions), and the like. “Slurry” as used herein, refers to divided solids in a continuous liquid phase.)
Chocolate also may have different forms. For example, milk chocolate is a confection that contains milk solids, milk fat, chocolate liquor, a nutritive carbohydrate sweetener, cocoa butter and may include a variety of other ingredients such as emulsifying agents, flavorings and other additives. Crumb chocolate is a type of milk chocolate wherein wet milk, carbohydrate sweetener ingredients and, optionally, chocolate liquor are combined and then co-dried at elevated temperatures to form a milk crumb. The crumb is then processed into crumb chocolate.
Many different types of chocolate are identified on the basis of the relative amounts of milk or other dairy solids, chocolate liquor, cocoa solids and fat (mainly cocoa butter) contained in them. In some cases, types of chocolate can also be identified by the method used in manufacture or the suitability for a given end use. The type of chocolate used to make M&M's brand chocolate candies herein defined as “convenience chocolate,” for example, is characterized by its relatively large average grain size of 40 microns. Typical fine chocolates have an average grain size less than 20 microns. Convenience chocolate also has a strong taste, making it suitable for use in confections such as M&M brand chocolate candies. Enrobing chocolate, which is liquid chocolate poured over other confections followed by solidification by cooling, has specific requirements: including a relatively low viscosity of 10,000 centipoise or less and low yield value.
The physical and textural properties of an edible, fat-based slurry or emulsion, such as chocolate, depend on the size of particles in the mixture and the degree to which the dispersed particles are mixed with the fat phase. These properties are conventionally controlled, at least in part, by grinding the particles to reduce their size and controlling the intimacy of mixing of the ingredients. Such grinding and mixing are related but distinct operations. In chocolate making, the grinding operation is typically performed on relatively low fat components in a roll refiner after which fat (cocoa butter) is added. The composition is then intimately mixed in a conche.
More particularly, this conventional process of manufacturing chocolate involves coarse grinding cocoa nibs into cocoa liquor, adding dried milk powder, sugar and some additional cocoa butter and then refining or fine grinding the mixture. The typical viscosity of a 28% fat slurry of 100-200 microns is 70,000 centipoise. The fine milling of this 28% fat slurry to 40 microns with a roll refiner converts the mixture to a sticky powder at 40 C.
A roll refiner is a precision machine usually comprising five rolls mounted vertically with the bottom feed roll offset from the other rolls. The rolls are made of cast steel and must meet extremely close tolerances with respect to their shape and surface characteristics. The operational tolerances of the roll refiner, including the distances between the rolls, the speed at which the different rolls rotate, the rate at which the rolls are cooled, and like considerations, similarly are small. Failure to operate within these tolerances can produce poor production results. A roll refiner must also be frequently cleaned and lubricated in order to operate properly. Accordingly, use of a roll refiner to make chocolate has certain disadvantages.
Further, after grinding in a roll refiner, the resulting paste is subjected to conching, or slow mixing, in a conche. In this operation, cocoa butter along with emulsifiers such as lecithin are added to and mixed with the ground particles, to form a reduced viscosity mixture. Whereas grinding in the refiner reduces particle size of the ingredients and increases viscosity, mixing of the ground paste and cocoa butter in the conche produces an intimate mixture of the ingredients, including the fat phase, to obtain lower viscosity at constant particle size. While the particle size may be somewhat reduced in the conche, the overall mixing process nevertheless lowers the viscosity of the chocolate ingredients.
The mixture is then worked in the conche at elevated temperatures to remove volatile ingredients and mellow the flavor and texture of the chocolate. Although many designs of conching equipment are known, the vast majority are batch machines, and all of them require substantial time, energy and labor to operate. Again, therefore, use of a conche has certain additional drawbacks.
A machine called the MacIntyre refiner/conche has also been used to make chocolate from raw ingredients. This equipment employs rotating scrape blades to simultaneously mix and crush the ingredients in the chocolate recipe in batch fashion. Although use of the MacIntyre refiner/conche is generally regarded as a simple and inexpensive way to make chocolate, the process performed by this unit is characterized by long batch times, which limit capacity. In addition, its operation and maintenance are complex.
Another alternative chocolate manufacturing apparatus is the so-called Wiener processor, which incorporates a ball mill to reduce or eliminate the need for a conventional roll refiner to produce ground chocolate particles. The components of the Wiener processor are the ball mill (known as a Wieneroto mill), a mixer conche and a “taste improver”. The ball mill comprises a cylinder housing rotors and steel grinding balls. Material is pumped into the base of the cylinder at relatively high pressure thereby filling the cylinder. The material is then subjected to the grinding action of the balls, which are set in rotary motion by the rotors. The cylinder is ordinarily completely filled with material so that no empty head space remains. The particle size of the cocoa solids in the chocolate recipe is progressively reduced as the mixture traverses upwardly in the cylinder, and is separated from the grinding balls by a screen at the top of the cylinder. The mixture is then cycled between a mixing conche and the ball mill to obtain the chocolate emulsion. In the taste improver, thin streams of the product are exposed to heated air across their surface. This operation reduces moisture content, reduces viscosity and yield value and removes volatile constituents. Although the Wiener process eliminates the refining stage associated with conventional processes in which a roll refiner is used, operation of the ball mill itself is problematic. The process thus performed is complicated and does not eliminate conventional conching. In addition, high intensity grinding in the mill typically raises the temperature of the materials contained in it significantly, which can result in burning of the sugar components.
Given the state of the art described above, there is a long felt need for technology that can perform grinding and mixing of fat based materials in a single unit and that will thereby reduce the cost and complexity of chocolate manufacturing processes by reducing the reliance on the refiner, conche, or both.